The systems used in the field of file transfer with no size limit in a strongly distributed IP network environment generally consist of a source server terminal and numerous target client terminals connected by “switches” and/or routers.
FIG. 1 diagrammatically represents a system of the type of that to which the invention applies. In such a system, a server 1 has a file 2 that has to be transferred via a transmission network 3 to a set of clients 4 which store this file on a corresponding disk, all the duly stored files being referenced 5. In this diagram, in the interests of the clarity of the drawing, the switches and/or routers that are part of the network 3 are not represented.
The downloading of the information must be done as quickly as possible, reliably, while reducing network usage time and avoiding unnecessary transfers.
The current FTP solutions, ssh/scp, propose a transfer time that is proportional to the number of clients. By using a machine tree structure comprising distinct network strands, the transfer times are proportional to the base 2 logarithm of the total number of machines: t=tu×log2(N), with t being the total time to load all the target machines, tu the time to transfer a file from point to point and N the number of target machines. This remains insufficient in usage contexts in which the unavailability time of the computer system is costly (civil avionics) or directly linked to the safety of individuals (health, defence).
There are faster solutions which use connectionless protocols and broadcast addresses, but they do not guarantee that the data sent will be received and do not propose retransmission mechanisms. Their lack of reliability confines them to niche applications.
When the files already exist on the targets, it is necessary to determine whether they are up to date or whether a new version of these files must be transferred; there is no reliable file comparison, prior to transfer, incorporated in the existing protocols. Unnecessary transfers are therefore commonplace.
The retransmission for each client of the same information means that, as seen from the network, the file transits a large number of times, which means mediocre performance and computer security issues.